1) The power switch.
This would only work if we knew it was coming and were given a few years to sort everything out. It would undoubtably provide a great movement towards creating infrastructure and everything that goes with that and comes afterwards but without the planning before hand it would take at least a third of the available time for it to begin and probably half of the available time before it was put to use properly. It would then be subject to the failures of any major project (Edinburgh trams, for example) and as such I reckon it would be quite a waste.
We'd need to train people to be able to use such a 'power'.
2) Justice
Everyone (of legal age) has committed a crime. Therefore, this is entirely stupid.
3) Oil substitute
Would destroy nations and companies who are reliant on oil production. Major Western Countries (particularly the Dutch, UK and USA) wouldn't be able to survive such competition and would therefore detremiate our lives drastically. Capitalism would fail, and ultimately we'd revert back to a sort of pseudo dark ages before the major industrial powers 'pre crash' would return and history would repeat itself. Therefore, entirely pointless and probably the most dangerous on the list.
4) The environmental switch
Possibly a good one, but again subject to the limitations of the first option. To much doubt at the moment about the effects of greenhouse gases and governments willingness to take action against them. Let us have this switch in 25 years time (that is, let us be aware we have the option) then it would perhaps be beneficial to build up a large nuclear option but if we're looking at a humanity issue it would benefit the rich western countries so much more than anyone else and what would happen with the masses of waste afterwards? So, based on a utilitarian view it's probably not going to be that great.
5) Anti-aging pill
Incredibly stupid. World is already over populated. It's the greatest threat to the World/mankind. We don't need, nor can we have, people living longer and longer with the birth rate as it is.
6) The teleporter.
Can't see any practical application apart from for military uses and as such can't see how it would be useful.
7) The cleanser
Would mean the destruction of so many painkillers and other beneficial drugs. I can see the usefulness in removing drug addiction but in reality this would mean addicts would redirect their addiction to other things that this beam did not destroy.
8) The producer
I'm assuming this is some sort of GM food thing. Yes, it's a great idea. Pollination is the issue here and if we can ensure that beneficial animals aren't killed off due to the lack of food sources then this is a clear winner. However, I'm not sure that we can do such with present science.
9) The cure
CV and infection are the top two iirc. To go back to number 5, the World is already overpopulated so this is a dangerous proposition. More people that live, more resources are used and as we have finite resources it will ultimately result in more deaths. So no.
10) The answer
It doesn't matter if a 'God' exisists or not, if it gives people belief then that's that. If having faith is good for you then I don't see any reason why it has to be disproved. Can't see any use in this whatsoever. We'd quickly find something else to fight over.